The present invention relates to an inside grindstone having an annular substrate whose inner periphery is formed with a cutting-edge layer, and to a method of washing the inside grindstone.
In a wafer processing technique in which a semiconductor material in the form of an ingot is cut to form a plurality of wafers, it is an important matter to reduce a machining allowance at cutting and to secure parallelism and surface roughness. For this reason, cutting operation is done by an inside grindstone.
At present, the following inside grindstone is used for processing wafers. That is, the inside grindstone comprises an annular substrate which is made of stainless steel or the like and which has its thickness of 100 .mu.m to 150 .mu.m. The annular substrate has its inner periphery which is formed with a cutting-edge layer, using diamond abrasive grains, by means of a bond that is electrodeposition bond such as nickel or the like. The cutting-edge layer has its thickness of approximately 250 .mu.m to 300 .mu.m and its width of approximately 2 mm to 5 mm.
FIGS. 5 and 6 of the attached drawings show a construction of the conventional inside grindstone. The conventional inside grindstone 100 comprises an annular substrate 101 whose inner periphery is formed with a cutting-edge layer 102. In order to facilitate discharge of shavings generated at cutting operation and washing of the inside grindstone 100, the thickness of the cutting-edge layer 102 is so formed as to be gradually thinned from an inner periphery 102a of the cutting-edge layer 102 toward an outer periphery 102b thereof.
The inside grindstone 100 is mounted to a vertical cutter or the like at processing of the wafers, and the cutting operation is done while abrasive is blown against the cutting-edge layer 102. At this time, shavings, which are generated by cutting of a brittle semiconductor material (hereinafter referred to as "work") such as silicon or the like, are minute or fine particles in the form of acute angle, which have grain size equal to or less than 1 .mu.m and which are difficult to flow. Further, the abrasive blown against the cutting-edge layer 102 is scattered toward the outer periphery of the annular substrate 101 by the inside grindstone 100 which is rotated at high speed. Accordingly, there are the following drawbacks or disadvantages. That is, it is impossible for the inside grindstone constructed as above to exhibit sufficient discharge and washing effects. Loading occurs at the cutting-edge layer 102, particularly, at the inner periphery 102a which exerts a great influence upon the cutting efficiency, so that the cutting performance is reduced. Moreover, since unreasonable stress acts upon the work, a layer of processing change in quality at the work surface increases in thickness.
When the loading occurs at the inner periphery 102a so that the cutting resistance increases, the cutting-edge layer 102 is swung or oscillated laterally so that the lateral side of the cutting-edge layer 102 is in contact with the work. Accordingly, the cut surface of the work is inadvertently shaved so that parallelism and surface roughness are damaged. Further, the annular substrate 101 per se is gradually deformed by an external force which acts upon the annular substrate 101 from the lateral side of the cutting-edge layer 102. Thus, the cutting-edge layer 102 is brought to such a state that the cutting-edge layer 102 further tends to be in contact with the cut surface of the work.
Deformation of the annular substrate 101, which is increased by the above-described vicious circle, increases the substantial thickness of the cutting-edge layer 102 so that the machining allowance of the work is made large. Thus, the parallelism and the surface roughness of the cut surface of the work are damaged. Further, the layer of processing change in quality also increases gradually so that the quality of the cut wafers is considerably reduced.
The drawbacks of the kind referred to above in the conventional technique become further intensified, accompanied with an increase in diameter of the work or ingot. In the present stage, the operator intends to cope with such drawbacks by a method or the like in which the deformation of the annular substrate 101 is monitored to suitably apply dressing to the inside grindstone 100. However, no sufficient effects are obtained. Further, the following drawback also occurs. That is, frequent dressing operations reduce the cutting efficiency per se, and the service life of the grindstone is also reduced.